Arthritis is a major cause of disability. Of the nearly 70 million persons in the US with arthritis and/or chronic joint symptoms, nearly 8 million are disabled because of their arthritis. Knee osteoarthritis (OA) and rheumatoid arthritis (RA) are two of its most common and disabling forms. Despite evidence that physical activity can improve functional and health related quality of life (HRQOL) outcomes and lower health care costs, the proportion of the US population engaging in the recommended amount of physical activity is low and even lower among those with arthritis. Moreover, there is considerable variation in clinicians' promotion of physical activity for arthritis clients. Care providers infrequently ask clients about their physical activity behavior and report feeling unprepared to promote physical activity. This application studies the effects of a behavioral intervention aimed at promoting physical activity, including lifestyle physical activity, on arthritis-specific and generic HRQOL outcomes. The proposed physical activity management program (PAM) is based on a chronic care model in which allied health professionals promote patient self-management activities outside of traditional physician office encounters. The program is an individualized counseling and referral intervention, conducted by physical activity managers, directed by a theory-based comprehensive assessment of individual patient barriers and strengths related to physical activity performance. The specific aims of this randomized, controlled trial of 480 clients with RA and knee OA followed for 24 months are to test the effectiveness of physical activity management combined with physician physical activity promotion (PAM group) compared to physician physical activity promotion only (control group) in improving arthritis-specific and generic HRQOL, observed measures of function, and objectively measured and self-reported physical activity levels. In addition, exploratory analyses will be done to assess whether the improvements in HRQOL and physical activity performance associated with the PAM program are mediated by increases in physical activity levels and theory-based motivational variables, respectively. This study is intended to generate feasible methods by which health care providers and health care systems can increase physical activity levels in clients with arthritis and to result in widely applicable strategies for health behavior change.